The coelom and the origin of the annelid body plan
|acoclomate; Annelida; Bilateria; body cavity; CELLS; coelom; EVOLUTION; Marine & Freshwater Biology; MUSCLE DEVELOPMENT; myoepithelium; ORGANIZATION; peritoneum; Polychaeta; pseudocoelomate; SYSTEMS; ULTRASTRUCTURE
The biphasic life cycle in annelids is characterized by two completely different types of organisation, i.e. the acoelomate/pseudocoelomate larva and the coelomate adult. Based on this observation the recent literature on the different assumptions on the organisation of the bilaterian stem species with special emphasis on the evolution of the annelid body plan is reviewed. The structure of the coelomic lining ranges between a simple myoepithelium composed of epithelio-muscle cells and a non-muscular peritoneum that covers the body wall muscles. The direction of the evolution of these linings is discussed with respect to coelomogenesis. As the coelom originates from mesodermal cell bands, different assumption on the acoelomate condition in Bilateria can be substantiated. The origin of segmentation in annelids is explained by current hypothesis. Although no final decision can be made concerning the origin of the annelid body plan and the organisation of the bilaterian stem species, this paper elaborates those questions that need to be resolved to unravel the relation between the different body plans.
Symposium on Morphology, Molecules, Evolution and Phylogeny in Polychaeta and Related Taxa, Osnabruck, GERMANY, SEP, 2002
Show full item record